1. Field of the Invention
The present invention relates to a liquid discharge apparatus which has a liquid discharge head to be electrically connected to a printed circuit board and in which an inspection for an electrical connection between the printed circuit board and the liquid discharge head is available, a connection inspecting method for the liquid discharge apparatus, and a production method for the liquid discharge apparatus.
2. Description of the Related Art
A liquid discharge apparatus such as an ink-jet printer is provided with a liquid discharge head including nozzles through which a liquid is discharged and a piezoelectric actuator as an example of the pressure-applying mechanism which applies the discharge pressure for discharging the liquid from the nozzles. The liquid is selectively discharged from the nozzles toward a printing medium when the piezoelectric actuator is driven so as to print an image, letters and the like on the printing medium. The piezoelectric actuator is provided with connecting terminals as input terminals. The connecting terminals are electrically connected to terminals of the printed circuit board on which a driver IC is mounted, by the aid of a conductive metal such as solder.
When the piezoelectric actuator and the printed circuit board are connected to one another by using the solder, firstly, the surface of the printed circuit board is masked with a solder resist or the like so that only the terminals of the printed circuit board are exposed, and then the solder is applied onto the terminals. Usually, the solder resist is used as the mask in a state of being cured or solidified. However, the solder resist has such a property that the solder resist is shrunk upon the curing or solidification. Therefore, the following problem arises. That is, the portion on the surface of the printed circuit board is shrunk by the solder resist, and the printed circuit board is curved (warped) and deformed. In a known printer, a piezoelectric actuator and a printed circuit board can be electrically connected to one another without using any solder in order to avoid the problem as described above. The printer is provided with the piezoelectric actuator which has protruding bumps to serve as input terminals and the printed circuit board which has terminals to be connected to the bumps. The surface of the printed circuit board, on which the terminals are formed, is covered with a synthetic resin layer. When the piezoelectric actuator and the printed circuit board are connected to one another, the printed circuit board is pressed against the piezoelectric actuator in a state in which the synthetic resin layer is uncured. In this situation, the bumps penetrate through the synthetic resin layer to be brought in contact with the terminals. The synthetic resin layer is cured while the bumps are brought in contact with the terminals, and thus the printed circuit board and the piezoelectric actuator are physically connected to one another. Accordingly, it is possible to avoid the connection of the printed circuit board to the piezoelectric actuator in a state in which the printed circuit board is curved and deformed. Therefore, the printed circuit board is easily handled when the connection is performed.
It is noted that the following problem may arise in relation to the connection between the piezoelectric actuator and the printed circuit board. For example, the bump fails to penetrate through the synthetic resin layer until the bump is brought in contact with the terminal, and the bump and the terminal are not in contact with each other in some cases, which is caused by the insufficient pressing force to be applied when the connection is made. In other cases, the bump and the terminal are separated from each other, which is caused by the deterioration of the synthetic resin layer due to the moisture or water contained in the atmospheric air. In such situations, the electrical resistance is increased between the bump and the terminal. Therefore, the current, which is required to drive the piezoelectric actuator, is not allowed to flow sufficiently from the power supply in the body. The piezoelectric actuator cannot be driven to discharge the liquid from the nozzles. Therefore, in order to inspect the change of the electrical resistance as described above, an exclusive inspection apparatus has been hitherto used. The inspection apparatus inspects the resistance of the connecting portion between the bump and the terminal such that a pair of inspection probes are brought in contact with the bump and the terminal as the inspection objectives respectively, and the current is allowed to flow from one inspection probe in this state to measure the current allowed to flow through the other inspection probe. Therefore, when the electrical resistance between the bump and the terminal is inspected, it is necessary to perform the inspection such that the pair of inspection probes are expressly brought in contact with the bump and the terminal corresponding to each of the nozzles. A problem arises such that the inspection requires the time and labor.